1. Field of the Invention
The present invention relates to a storage device and an information processing apparatus which are connected to a network.
2. Description of the Related Art
In recent years, instead of a form of directly coupling a storage device to a computer (hereinafter also referred to as “host”), a form of connecting one or more storage devices to a plurality of hosts via a network has been frequently used. This connection form for storage devices using a network is called a storage area network (hereinafter referred to as “SAN”). The SAN has been constructed by using a fibre channel (hereinafter referred to as “FC”) technique so far. An FC-based SAN is referred to as an FC-SAN.
In the case in which the FC-SAN is constructed, in order to improve availability of an entire system, a host and a storage device are connected by a plurality of physical communication paths (hereinafter also referred to as “paths”). The host sends commands and data to the storage device using the respective paths to thereby balance loads on the paths. Examples of an algorithm for determining a ratio of use of a plurality of paths include a weighted round-robin with which commands and data to be sent are allocated to the respective paths at different ratios (e.g., 60% of commands to be sent are allocated to path 1 and 40% of commands to be sent are allocated to path 2). In addition, in the case in which it is detected that one path has become unusable due to a cause such as a failure of a switch constituting the FC-SAN or disconnection of a network, the host continues communication with the storage device using the remaining paths.
The load balancing among paths as described above is carried out not only in communication between a host and a storage device (hereinafter referred to as “host-to-storage communication”) but also in communication between a storage device and another storage device (hereinafter referred to as “storage-to-storage communication”). Examples of the storage-to-storage communication include remote copy. The remote copy is a technique for transferring data, which is stored in a storage device, to another storage device set in a geographically distant site to copy and save the data.
One of path control techniques in the above-mentioned host-to-storage communication is disclosed in JP-A-2000-330924.
On the other hand, an IP-SAN has been attracting attention. IP-SAN is constructed by using a network adopting the Internet protocol (hereinafter referred to as “IP”) (hereinafter referred to as “IP network”) which requires less acquisition costs than an FC. In the case in which a host communicates with a storage device via the IP-SAN, iSCSI, which is a protocol encapsulating an SCSI protocol with TCP/IP, is mainly used.